1. Field of the Invention
The present invention relates to a film forming method for forming a planarized interlayer insulating film to cover wiring layers, etc. of a semiconductor integrated circuit device, and a semiconductor device manufacturing method using such film forming method.
2. Description of the Prior Art
In recent years, in the field of the semiconductor integrated circuit device, a higher integration density is proceeded and the case where a multi-layered wiring extending to several layers or more is formed is increased. In this case, since especially aluminum material is often employed as a material of the wiring layer, a film forming method which makes it possible to form a planarized interlayer insulating film at the low temperature of less than 500.degree. C. is earnestly requested.
In the planarizing method by using the heating/fluidizing process, perfect filling of the interlayer insulating film can be expected because thermal fluidability is employed. At present, especially the BPSG (Boronphosphosilicate Glass) film is often used in such application. But the heating at the temperature of 850.degree. C., even if the lowest temperature is selected, is needed to fluidize the BPSG film. Therefore, the BPSG film cannot be applied to the applications as the underlying layer of the wiring layer and the interlayer insulating film, both being requested to be formed at the low temperature, especially the application as the insulating film covering the aluminum wiring layer.
In this case, the fluidization temperature can be lowered to some extent by increasing the phosphorus or boron concentration. However, such fluidization temperature is not enough and in addition such a new problem is caused that stability and moisture resistance of the insulating film is reduced. Since the substantially same fluidization temperature as that in the BPSG film is needed for the PSG (Phosphosilicate Glass) film, the above problem is similarly caused.
Also, as the insulating film having the low fluidization temperature, the GeBPSG film in which GeO.sub.2 is added to the BPSG film has been developed. But the fluidization temperature can be merely lowered to about 750.degree. C. at best, and thus it is difficult to apply the GeBPSG film to the underlying film and the interlayer insulating film for which the low temperature treatment is requested.
For this reason, in Patent Application Publication (KOKAI) Hei 10-135203, etc., the film forming method which enables to form the planarized insulating film by lowering the fluidization temperature has been disclosed. The film forming method will be explained in the following.
First, as shown in FIG. 1A, the film-depositing substrate 101 (hereinafter merely referred to as substrate 101 as the case demands) is loaded into the chamber of the plasma CVD equipment or the thermal CVD equipment. Then, in the case of the thermal CVD equipment, the substrate heating is effected and then held at the predetermined substrate temperature. In this case, in the substrate 101, the underlying insulating film 2 made of the silicon oxide film, etc., for example, is formed on the silicon substrate (semiconductor substrate) 1 and then the wiring layers 3a, 3b made of the aluminum film, etc., for example, are formed on the underlying insulating film 2.
Then, as shown in FIG. 1B, the gas mixture consisting of the phosphorus containing compound, which has III valence phosphorus and in which oxygen is bonded to at least one bond of the III valence phosphorus, the silicon containing compound, and the oxidizing gas is prepared as the film forming gas. This film forming gas is introduced into the chamber and plasmanized, and held for a predetermined time. Accordingly, the PSG film 5 of predetermined thickness, which contains high density of P.sub.2 O.sub.3, can be formed. At this time, according to the density of P.sub.2 O.sub.3 and the rate of P.sub.2 O.sub.3 /P.sub.2 O.sub.5, sometimes the PSG film 5 is fluidized at the substrate temperature during film formation. In this case, the planarization can be achieved simultaneously with the film formation.
If not so, as shown in FIG. 1C, after the PSG film 5 has been formed on the substrate 101, the heating process is executed separately to fluidize the PSG film 5 and thus planarize a surface of the PSG film 5. In this case, since the PSG film 5a having the high density of P.sub.2 O.sub.3 is formed as a phosphorus component, the fluidization temperature can be lowered widely to less than 500.degree. C. Therefore, such PSG film 5a can be utilized as the interlayer insulating film covering the aluminum wiring.
By the way, since P.sub.2 O.sub.3 itself can react easily with the moisture, the PSG film 5a absorbs the moisture if the PSG film 5a is picked out into the air in the above steps, e.g., when the process is switched from the film forming step of the PSG film 5a to the planarizing process step, or if the PSG film 5a is taken out into the air after the film formation, whereby reduction in film quality of the PSG film is brought about.
Therefore, in order to utilize the PSG film 5a as the interlayer insulating film of the semiconductor device, etc., the PSG film 5a must be stabilized such that the moisture absorption of the PSG film 5a should be prevented in the middle of the film forming steps of the PSG film 5a and also after the PSG film 5a has been formed.